1. Department of Economics, University of Mannheim, L7, 3–5, Mannheim 68131, Germany
2. IFAU Uppsala, Uppsala, Sweden
3. VU University Amsterdam, Amsterdam, Netherlands
4. IZA, Bonn, Germany
5. University of Rostock, Rostock, Germany
6. Max Planck Institute for Demographic Research, Rostock, Germany
7. The Danish Twin Registry, and The Danish Aging Research Center, University of Southern Denmark, Odense, Denmark